Through injury or diseases, human or animal lungs can become too weak to sustain a sufficient flow of oxygen to the body and to remove adequate amounts of expired carbon dioxide. Under these circumstances, it is often necessary to aid the lungs through forms of mechanical assistance, such as mechanical ventilation.
In a common form, mechanical ventilation involves the introduction of an endotracheal tube and, in some cases, a small, open-ended catheter within that tube, into the trachea of a human or animal. The distal ends of the endotracheal tube and/or catheter are positioned to rest at or slightly above the carina of the lungs. A well-humidified oxygen/air mixture is then introduced through the endotracheal tube and/or catheter to provide oxygen to the lungs. In less severe circumstances, the oxygen/air mixture can be supplied through the endotracheal tube and/or catheter using continuous positive airway pressure (CPAP). Where CPAP is used, the patient will use his or her own lung power to exhale the inspired gas. In more severe circumstances, it is necessary to use mechanically controlled ventilation with a positive end expiratory pressure (PEEP).
One problem commonly associated with the use of endotracheal tubes is the accumulation of mucus on the inside walls of the endotracheal tube. In a healthy human, mucus is secreted through glandular action in the trachea/bronchial tree and is progressively transported upward through the action of cilia along the tracheal airways. Upon nearing the vocal folds, such mucus is either swallowed or expectorated.
This mucus transport mechanism is generally not available, though, to a patient intubated with an endotracheal tube. Typically, the endotracheal tube will block the mucus clearing action of the adjacent cilia, particularly where an inflatable cuff is used to firmly position the endotracheal tube against the inside wall of the trachea. In such case, instead of being expelled from the lungs and trachea, the mucus will tend to migrate up from the bronchia tree through the distal end of the endotracheal tube and then collect on the inside walls of the endotracheal tube. If such mucus collection is allowed to continue, the internal diameter of the endotracheal tube will become smaller, which makes it more difficult to breathe. Perhaps more seriously, infectious bacteria (e.g., Staph and Pseudomonas spp.) tend to grow and multiply on the stagnant mucus. The bacteria infected mucus can then aerosolize and deposit into the patient's lungs, leading to ventilator-associated pneumonia.
A number of approaches have been developed to address the mucus accumulation problem for endotracheal tubes. In the most basic approach, the mucus laden endotracheal tube is simply removed from the patient's trachea and replaced with a clean endotracheal tube. Needless to say, removing the mucus laden endotracheal tube is very uncomfortable for patient, particularly since ventilation must be interrupted during the removal process. Moreover, reinsertion of a clean endotracheal tube can lead to tracheal injury, particularly if it is done frequently.
In another common approach, salt water is introduced into the endotracheal tube to dissolve the mucus and a suction catheter is then inserted into the endotracheal tube to try to vacuum up the dissolved mucus deposits. This suctioning approach has a number of drawbacks. First of all, the suctioning process typically takes 10 to 15 seconds to complete, which can seem like an agonizingly long time for many patients. Secondly, the suction catheter tends to miss a number of the accumulated mucus deposits and thereby leaves them as a breeding ground for infectious bacteria.
A further approach to the mucus accumulation problem is described in the lead inventor's U.S. Pat. No. 5,687,714. In this approach, droplets of water or saline are entrained in the oxygen/air ventilation mixture to continually dissolve mucus before it has an opportunity to form deposits and a reverse thrust catheter is used to help transport dissolved mucus away from the lungs.
Recently, the lead inventor has developed a mucus shaver cleaning apparatus which is described in co-pending patent application Ser. No. 10/773,570, the disclosure of which is hereby incorporated by reference. This mucus shaver cleaning apparatus comprises a central flexible tube with an inflatable balloon at its distal end. Affixed to the inflatable balloon are one or more shaving rings, each having a squared leading edge to shave away mucus accumulations. In operation, the uninflated cleaning apparatus is inserted into the endotracheal tube until its distal end is properly aligned with or slightly beyond the distal end of the endotracheal tube. After proper alignment, the balloon is inflated by a suitable inflation device, such as a syringe, until the balloon's shaving rings are pressed against the inside surface of the endotracheal tube. The cleaning apparatus is then pulled out of the endotracheal tube and, in the process, the balloon's shaving rings shave off the mucus deposits from the inside of the endotracheal tube.